Magnesium vs Vitamin D for cognition: which has better evidence?
A tie on evidence grade for cognition (Magnesium Grade C vs Vitamin D Grade C). For cognition, the two are evidence-matched; the difference is in effect and safety.
Platform evidence comparison
These existing platform assessments are separate from the source-reported findings below. They do not represent a direct trial comparing these treatments.
| Magnesium | Vitamin D | |
|---|---|---|
| Grade | grade C | grade C |
| Certainty | low | low |
| Effect | Systematic review of magnesium and cognitive health in adults: the evidence linking magnesium status or intake to cognition is limited and inconsistent, drawn largely from observational data, and the authors call for better-designed studies with repeated magnesium biomarkers before any conclusion. No demonstrated cognitive benefit from supplementation. | Systematic review and meta-analysis: lower vitamin D levels are associated with poorer cognition and higher dementia risk. The association is mostly observational; supplementation trials have not established that raising vitamin D improves cognition. |
| Studied dose | not standardized | not applicable — observational association |
| Population | adults | older adults |
| Safety | 1 modeled interaction(s) | 1 modeled interaction(s) |
Grade C / low: hints of benefit in small trials; a well-run RCT could easily push this to B or to null.
Direct comparison evidence
There are no direct RCTs in our corpus comparing Magnesium and Vitamin D head-to-head for cognition. What we present above is an indirect comparison: each side's own trials, contrasted. This is standard practice for supplement comparisons — dose, population, and outcome-instrument differences between the two evidence bases add uncertainty on top of each side's own grade.
Can you take both?
Modeled interaction: minor. Magnesium is a cofactor in vitamin D metabolism; the two are complementary. Full interaction page →
Decision guidance
- If certainty matters most — choose whichever side carries the higher certainty rating at a similar grade.
- If you're on medications — check each side's interaction pages before deciding; safety differences dominate small evidence-grade gaps.
- If your population is under-studied — the smaller-effect side with better population evidence often wins over the higher-grade side studied in a different demographic.
- If cost matters — form and dose page differences (Magnesium vs Vitamin D) can invert the practical winner.
Grade history
No grade changes yet. Initial grade assigned; re-reviewed on every 6 months (Grade C+) — next review by . Methodology v1.
Re-review cadence: every 6 months (Grade C+) · next scheduled by · methodology v1.
Frequently asked
Which has stronger evidence: Magnesium or Vitamin D for cognition?
Magnesium carries Grade C at low certainty; Vitamin D carries Grade C at low. The stronger evidence points to a tie, subject to the caveat that direct head-to-head trials are usually absent for supplement pairings.
Can I take Magnesium and Vitamin D together?
Modeled interaction between Magnesium and Vitamin D: severity minor. Magnesium is a cofactor in vitamin D metabolism; the two are complementary.
Have Magnesium and Vitamin D been compared head-to-head?
Direct RCTs comparing the two for cognition are uncommon. This page contrasts each side's own trial evidence — that is an indirect comparison, which introduces confounds from population and dose differences. See the direct-comparison block above.
What decides between Magnesium and Vitamin D for me?
Read the decision guidance below — the split usually comes down to population fit, interaction risk with your other medications, and how much certainty you want behind the recommendation.
Related
Cite this page
Citation is encouraged. The proposed reuse license is CC-BY-4.0; status: pending-governance-ratification.
Plain-text citation
Substrate. Magnesium vs Vitamin D for cognition. https://evidencebased.info/compare/magnesium-vs-vitamin-d-for-cognition. Updated 2026-07-14.
BibTeX
@misc{substrate_vitamindforcognition,
author = {Substrate editorial},
title = {Magnesium vs Vitamin D for cognition},
year = {2026},
url = {https://evidencebased.info/compare/magnesium-vs-vitamin-d-for-cognition},
note = {evidencebased.info}
}